Roasted coffee material has long been known as a source of oil which is useful as an aroma carrier and which has been used for the aromatization of soluble coffee. It has, however, been recognized that coffee oil contains a variety of compounds, most notably diterpene esters, which renders coffee oil quite dissimilar from other vegetable oils, such as cottonseed oil. Thus, because of its dark color, distinct flavor and high diterpene content, coffee oil has not been considered as an edible vegetable oil. Now, however, due to the increased demand on the world supply of vegetable oils, alternative sources of supply are being considered. Since roasted coffee oil is readily obtained from roasted coffee, including water-extracted or spent roasted coffee grounds which are at present considered a waste product of the soluble coffee industry, it has become increasingly practical to consider converting crude roasted coffee oil into a refined or purified edible oil. Purification of coffee oil obtained from spent coffee grounds, is also beneficial for stability purposes since crude oil from spent grounds, is significantly less stable than oil from unextracted roasted coffee.
It may also be desirable to employ a purified form of coffee oil in various soluble coffee aromatization techniques since purified coffee oil may be superior, from an organoleptic viewpoint, to crude coffee oil as a carrier for condensed coffee aromatics such as grinder gas aroma. Purified coffee oil combined with condensed grinder gas aromatics has been found to contain less instances of rubber boot and petrochemical flavor notes than its crude coffee oil/grinder gas counterpart.
Crude coffee oil can be obtained by utilizing extraction methods well-known in the art to obtain the oil from roasted coffee material which may be either in the whole bean or comminuted (e.g. ground) condition. The roasted coffee may be either unextracted or water-extracted; it being recognized that water-extracted ground roasted coffee will supply the most economical source of oil.
Generally, two basic oil extraction methods are employed in the art. The first comprises a liquid extraction process where extractives such as hexane are utilized to remove coffee oil from the roasted coffee. In this process the extractive after contact with the roasted coffee is removed to yield a residue of coffee oil. However, the far more common process comprises expressing coffee oil from roasted coffee by subjecting the coffee to extreme pressure conditions. The product of this process is often referred to as "expressed coffee oil," and since expressed coffee oil has the advantage of not requiring the addition of foreign materials to obtain the coffee oil, expressed coffee oil is most often utilized in coffee processing.
Conventional alkali refining, normally used in the production of edible oils, has not been effective on coffee oil because of its high content of unsaponifiables. A method has been disclosed, however, for the refining or purification of coffee oil such as the high vacuum distillation technique of U.S. Pat. No. 3,704,132. It has been found, however, that purified coffee oil which comprises primarily triglycerides and which is substantially free of diterpene esters has poor stability to oxidative rancidity.
If fresh purified coffee oil is promptly added to soluble coffee, such as by spray plating, the resulting stability is satisfactory for a period of only about several weeks. If the purified oil is stored for a period prior to use, off-flavors or even rancidity rapidly develop.
This invention relates to a method of protecting or stabilizing purified coffee oil so that it might be stored for prolonged periods and used either as a general purpose edible oil or in the aromatization of soluble coffee.